1. Field of the Invention
The present invention relates to a test system used to align the boresite of a radar antenna. More particularly, the present invention relates to a test system that is used to align the boresite of an automotive radar system antenna with a mechanical reference (e.g., the thrust vector) from a vehicle on which the radar is mounted.
2. Description of the Related Art
Recently, manufacturers have begun producing radar systems for automobiles. Such systems have been used in combination with a vehicle cruise control to form an automotive radar system. An automotive radar system transmits a signal from an antenna typically located in the grill area of an automobile. The presence of and distance to an object from the automotive radar antenna is determined from the signal reflected by the object. If an object is detected in the path of the vehicle, wheel braking or engine deceleration is applied by the automotive radar system to maintain a desired distance from the object and to prevent the vehicle from striking the object.
To assure proper performance of a automotive radar system, the device must be regularly tested. During testing, proper alignment of the automotive radar antenna boresite angle with a mechanical reference line, such as a thrust vector of the vehicle which identifies the forward direction of travel of the vehicle, must be achieved. An automotive radar antenna boresite may become misaligned due to vehicle vibrations, vehicle collisions, or other factors. The boresite angle must be properly aligned to prevent the radar system from encountering false or inaccurate readings from signals received from vehicles in adjacent lanes, and to ensure proper detection of vehicles or objects in the immediate lane.
To align the boresite of the automotive radar antenna for FM-CW and Pulse modulated radar systems, a Doppler shifted signal is not generally required for the radar. A passive trihedral target reflector may be used for testing and mechanically aligned at a point in space along the vehicle thrust vector. With the trihedral target so aligned, the position and orientation of the antenna are set to maximize the energy reflected back to the automotive radar from the trihedral target.
Frequency shift keying (FSK) modulated radars require a Doppler shift in order for the radar to respond. To align the FSK radar along the vehicle thrust vector, either the vehicle must be moving relative to a trihedral target, or the target moving, and the antenna aligned to maximize reflected energy.
U.S. Pat. Application Ser. No. 09/252,492 discloses use of interferometers in combination with a transponder to perform alignment. The interferometers enable a display reading to be provided from the transponder so that an operator can align the boresite of the automotive antenna with the thrust vector of a vehicle using the display. The transponder also provides a return signal to the automotive radar to simulate an object at a desired distance from the automotive radar. The transponder can provide a Doppler shift enabling FSK modulated, as well as other types of modulated radar signals to be tested.